Sea surface temperature variability at the Argentinean and Uruguayan coast off the Rio de la Plata estuary: evidence of upwelling

SIMIONATO, CLAUDIA G.; LUZ CLARA TEJEDOR, MOIRA; MOREIRA, DIEGO; CAMPETELLA, CLAUDIA

Lisboa

Simposio; 10th International Coastal Symposium ICS2009; 2009

This paper discusses preliminary results of an analysis of SST variability in the coastal region of South America between 30 and 39° S that is largely influenced by the Rio de la Plata estuary’s plume, and its relation with wind variability. Data are six years of daily ensembles of gridded satellite SST and sea surface winds with spatial resolutions of about 11 and 25 kilometers, respectively. At the central estuary most of the variance is explained by the annual cycle, whereas in coastal areas of the exterior estuary almost 10% is due to other processes. A principal components (Empirical Orthogonal Functions, EOF) analysis shows that the seasonal cycle can be explained in terms of two modes. The first one, characterizing fall-early winter/spring-early summer is related to the radiative cycle. The second mode, corresponding to late winter and late summer, displays warm/cold anomalies along the Uruguayan coast which are forced by the prevailing winds during those seasons that advect either the estuarine or oceanic water. An EOF analysis of the SST variability in sub-annual scale shows that a large portion of its variance is also related to zonal wind anomalies that force warm/cold SSTs along that coast, but in shorter time scales. Cold events observed in summer display anomalies of up to -5°C and occur under anomalously intense eastern winds (parallel to the coast) thus suggesting upwelling. Those events were very frequent during the observed period and showed large persistence, occurring up to one month. Given that the Río de la Plata estuary is a spawning and nursery ground for numerous coastal species, these factors might play an important role on biological activity so as in sediments transport.